Cathepsins are a class of globular lysosomal proteases playing a vital role in mammalian cellular turnover. They degrade polypeptides and are distinguished by their substrate specificities. Cathepsin S is a cysteine proteinase involved in the pathogenesis of autoimmune diseases, atherosclerosis, cancer, obesity and related diseases.

The SensoLyte® 440 Cathepsin S Assay Kit uses a fluorogenic peptide for measurement of enzyme activity. This peptide releases the AMC (7-amino-4-methylcoumarin) fluorophore upon cathepsin S cleavage, and which can be detected with excitation at 354 nm and emission at 442 nm.